This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Vitamin D deficiency is widespread and linked to decreased bone mineral content. Little data exists regarding the vitamin D status and the relationship of 25-OHD status to functional bone health outcomes in Hispanic infants. To evaluate this, we plan an observational cohort of full term, healthy, exclusively breastfed Hispanic and Caucasian infants. We hypothesize serum 25-OHD measured in cord blood will be significantly lower in Hispanic than Caucasian infants, with 25-OHD <20 ng/mL found in at least 50% of Hispanic neonates. 25-OHD, ionized calcium, and parathyroid hormone will be measured on cord blood. Secondary aims evaluate the relationship between 25-OHD levels and bone mineral status at baseline and after 3 months of 400 IU/day supplemental vitamin D3. Whole body DXA and SOS U/S will be measured shortly after birth, then again after supplementation. Data from this study will provide information needed to design further randomized trials and interventions. Primary Aim: To evaluate the relative frequency of vitamin D deficiency in human milk fed Hispanic compared to Caucasian newborn infants in Houston, Texas. Secondary Aims: To determine if infant vitamin D status is related to bone mineral status at birth and to determine the effects of vitamin D supplementation on 25-hydroxyvitamin D (25-OHD) concentration and bone mineral status vitamin D deficient and vitamin D replete infants at 3 months of age. In recent years, severe vitamin D deficiency has resurfaced as a major public health concern. Nutritional rickets is widespread, and a recent report on this disease in Texas showed Hispanic children are at increased risk. Long-term follow-up has demonstrated that vitamin D deficient infants are more likely to have decreased bone mineral status in late childhood. Additionally, vitamin D deficiency has been linked to changes in fetal imprinting and increased susceptibility to autoimmune diseases, immune deficiency, and malignancy. At birth, an infant s vitamin D status is entirely dependent on the vitamin D status of the mother. Many studies have shown vitamin D deficiency is very common in mother-child pairs, especially in dark-skinned individuals. However, few data exist regarding the vitamin D status in Hispanic infants. Low milk intakes and decreased sun exposure with urbanization makes this a very high-risk group among infants in Texas.